Hemisphere dominance: sign language aphasia and sign language processing

Samenvatting

Hemisphere dominance for language seems to be a basic fact of human psychology. This may be related to supramodal representation of natural language systems. Alternatively it might be associated with transmodal processing and convergence being a prerequisite for human speech. The fact that sign languages and sound languages are based on different primary modalities (visualspatial for sign languages and oral-auditory for sound languages) provides the opportunity to compare the neurofunctional substrate of both language types in order to approach this problem. Empirical evidence can be taken from studies of sign language aphasia as well as from imaging studies exploring intact sign language processing. Up to now most known data document left hemisphere dominance for intact and defective sign language functions. Thus, empirical evidence appears to reject the hypothesis of language dominance to be dependent on the oral-auditory modality alone. We present additional evidence from a new imaging study on the perception of written and signed lexemes in deaf and hearing volunteers.